1. Field of the Invention
The present invention relates to a lead frame, and an optical communication module using the lead frame and a method for manufacturing the optical communication module.
2. Description of the Related Art
FIG. 10 is a cut-away perspective view showing a sectional structure of a semiconductor laser transmitter that is employed in related art. In a package, a semiconductor laser 10 (LD) and a monitor photodiode 15 (M-PD) for sensing its light intensity are disposed. A light signal output from the LD 10 is incident upon an optical fiber 61 via a lens 16. Such an optical communication module is called a coaxial type from such the structure.
However, the optical communication module of the coaxial type has a three-dimensional structure, and is limited in reducing the size and shortening the manufacturing process.
To solve this problem, a surface mounting technique for mounting the LD, the M-PD, the photodiode (PD) or a preamplifier (PRE-AMP) like a plane on the substrate has been developed. Referring to FIGS. 11 to 13, a manufacturing process of the optical communication module using this surface mounting technique will be described below. FIG. 11 is a plan view of the related-art lead frame, FIG. 12 is a flowchart showing a manufacturing process of the optical communication module, and FIG. 13 is an explanatory view for explaining a manufacturing method for the optical communication module.
A lead frame 120 is formed by plating Ni and Au plated successively on a copper plate having a thickness of 200 xcexcm. The lead frame 120 comprises a frame 121 like a framework, a die pad 122 connected via a lead 123 to the frame 121, and each lead 123 connected to a tie bar 124, as shown in FIG. 11.
The optical communication module using the lead frame 120 is manufactured through the manufacturing process as shown in FIGS. 12 and 13.
First of all, a Si platform having a V-groove for fixing an optical fiber 61 inserted into a ferrule 62 and an electrode pattern for soldering a LD 10 or M-PD 15 is prepared.
The LD 10 and the M-PD 15 are soldered onto the Si platform 30, and then the optical fiber 61 is fixed to the Si platform 30 by the resin. An intermediate product in this state is called a sub-module. At fixing the optical fiber 61, the optical fiber 61 is sandwiched between a glass plate 130 and the Si platform 30.
The sub-module is fixed onto the die pad of the lead frame 120, wire bonded and sealed with a resin 140 by transfer molding technique.
Next, the tie bar 124 and the frame 121 of the lead frame 120 are cut, each lead 123 is electrically isolated, and the lead 123 exposed from the package is bent at a predetermined angle.
After the lead frame is completed up to this state, an electric current can be firstly passed through the LD and the M-PD. A so-called screening is made by passing electric current through the LD under high temperature environment or applying an inverse bias to the M-PD. The LD is determined good or defective, for embodiment, depending on a variation of threshold current that is especially sensitive to the stress. The M-PD is determined good or defective, depending on a change rate of leak current. The final check of product is made after screening.
In this way, the optical communication module using the surface mounting technique is enabled to lower the costs and reduce the size, and expected to contribute to a further progress of the optical communication.
However, the related-art technique had the following problems.
In the optical communication module using a standard one-layer lead frame, the number of leads is limited, so that the optical communication function to be implemented is limited. For example, in a case where the LD and the LD driver IC are built into the transmitter, the PD and the PRE-AMP are built into the receiver, or both of them are integrated, the number of components to be mounted is increased, requiring a greater number of leads.
Accordingly, it is an object of the present invention to provide a laminated lead frame capable of packaging at high density.
It is another object of the invention to provide an optical communication module of small size and low costs, which is allowed to package the optical communication functions at high density, and prevent the leakage of resin in resin molding.
Moreover, it is another object of the invention to provide a method for manufacturing an optical communication module capable of packaging the optical communication functions at high density.
A laminated lead frame of the present invention comprises a plurality of lead frames and a tie bar made of an insulating material for holding the plurality of lead frames like a laminate.
The laminated lead frame at high packaging density can be provided by integrating the plurality of lead frames that are laminated by the tie bar (insulating tie bar) made of insulating material. In particular, there is no shortage in the number of leads even if a number of components are mounted to implement the satisfactory optical communication functions.
Also, an optical communication module of the present invention comprises a laminated lead frame having a plurality of lead frames and a tie bar made of an insulating material for holding the plurality of lead frames like a laminate, and an optical communication functional unit that is disposed on at least one layer of the lead frame.
A great number of components can be mounted, employing the laminated lead frame, and the optical communication module can have the full optical communication functions.
In related art, since the tie bar was made of the same metal material as each lead, with each lead being electrically in conduction, the screening was not enabled by passing a current through the LD and the M-PD individually before resin molding. In the present invention, the tie bar is made of an insulating material, the leads in each layer are electrically isolated, whereby the screening is enabled at the former stage before packaging. Therefore, it is possible to eliminate the waste in rejection that causes the increased costs, and reduce the costs of the product.
Herein, the optical communication functional unit has the functions of a transmitter or receiver for use in the optical communication, or a composite transmitter/receiver. For instance, the optical communication functional unit preferably comprises at least one of a light emitting element and a light receiving element and an optical transmission medium. The optical transmitting module may employ the LD as the light emitting element and a driver IC for the LD as the electric circuit component. Furthermore, the optical transmitting module may employ the M-PD for sensing the light intensity of the LD. The optical receiving module may employ the PD as the receiving element and an amplifier for amplifying a PD signal as the electric circuit component. The optical transmitting/receiving module may comprise at least one pair of light emitting element and driver IC, and at least one pair of light receiving element and amplifier. The optical transmission medium may be the optical fiber or optical waveguide.
The material for the tie bar is not specifically limited so far as it has an insulating property and an excellent productivity. The thermoplastic resin that is cured in short time and excellent in productivity is preferable. In particular, the tie bar is preferably composed of the liquid crystal polymer.
The optical communication functional unit is preferably mounted on a Si substrate or a ceramic substrate. Si allows the V-groove to be easily formed by etching, or the ceramic such as alumina, which has insulating property and high hardness, can be worked at high precision.
The optical communication functional unit is desirably accommodated within a resin molded portion. The optical communication functional unit can be protected by resin molding. A specific method for forming the resin molded portion is preferably the transfer molding. The resin for use with the transfer molding may be epoxy resin, for example.
Moreover, a method for manufacturing an optical communication module according to the present invention comprises preparing a laminated lead frame having a plurality of lead frames and a tie bar made of an insulating material for holding the plurality of lead frames like a laminate, mounting an optical communication functional unit on at least one layer of the laminated lead frame, and resin molding the laminated lead frame with the optical communication functional unit mounted with a mold, wherein the tie bar prevents a leakage of a molding resin from the mold in the resin molding step.
In the resin molding step, usually, an object to be molded is placed within a mold, and the resin is injected. With the lead frame of laminated structure, it is difficult to prevent securely the leakage of resin especially from between each layer of the lead frame. With the method of the present invention, the excellent resin molded portion without burr caused by the leakage of resin can be produced by using the insulating tie bar for holding each layer of the lead frame like a laminate as a weir for preventing the leakage of resin in the molding step.
The insulating tie bar may be cut or left behind after the molding step. In the case where the insulating tie bar is left, it may be exposed outside the resin molded portion, or may be integrated with the molding resin to constitute a part of the outside shape of the resin molded portion.